Recently, the Federal Communications Commission (FCC) has approved that unlicensed radio transmitters can operate in the broadcast television spectrum at locations where that spectrum is not being used by licensed services (this unused TV spectrum is often termed “white spaces”) under certain rules. It can be expected that the implementation of Cognitive Radio (CR) in TV white space will be a major topic within wireless communication into the future. Cognitive Radio was introduced to implement negotiated, or opportunistic, spectrum sharing to provide a viable solution to the problem of sparsity of the wireless spectrum. In 2004, based on the expectation of unlicensed use of TV white space, under the charter of an IEEE 802 Standards Committee, a working group named IEEE 802.22 was established to develop a standard for a Cognitive Radio-based PHY/MAC/air interface for use by license-exempt devices on a non-interfering basis in spectrum that has already been allocated to the TV Broadcast Service. The IEEE 802.22 working group is also called the WRAN Group, since it is essentially developing an air interface for a Wireless Regional Area Network (WRAN) with a range as large as 30 miles. To implement CR systems that will not interfere with licensed signals, it is important to be able to detect the presence of licensed signals under very low signal-to-noise ratio (SNR) conditions. To this end, the IEEE 802.22 WRAN Group established a sensing tiger team to be responsible for the development of spectrum sensing methodologies. The TV broadcast signal in North America was under transition from analog to digital and the transition ended on Jun. 12, 2009. The Digital TV (DTV) signal is 8-PAM employing a Vestigial Sideband (VSB) modulated signal specified by the ATSC Digital Television Standard. Therefore, the main task in spectrum sensing for IEEE 802.22 WRAN is to detect the existence of the ATSC-specified signal in the TV bands. Besides the US Office of Communications (Ofcom), independent regulators and the competition authority of the communication industries in the United Kingdom, have considered license exempt use of interleaved TV spectrum for cognitive devices in December 2007. The DTV signal in Europe is an OFDM-based signal defined by the Digital Video Broadcasting-Terrestrial (DVB-T and DVB-T2) Standards. There are also many existing or progressing standards which adopt an OFDM transmission technique. There are existing sensing algorithms in the prior art, including those proposed to the WRAN Group. Most of these sensing methods can only be used for ATSC DTV signals. One prior art method using a power detector does not work when the SNR is below −3.3 dB because of a noise uncertainty issue. Another prior art method using an eigenvalue-based algorithm typically cannot distinguish between interference signals and licensed signals. As a result, a robust spectrum sensing algorithm which is dedicated to OFDM modulated signals is highly desired. Most of the existing OFDM spectrum sensing methods make use of the Cyclic Prefix (CP) or cyclostationarity of OFDM signals. There are different ways of introducing cyclostationarity in OFDM signals, e.g., by the use of Cyclic Prefix (CP), or by the use of different transmit powers on the subcarriers. Among these ways, the cyclostationarity property of the OFDM signals is most significant due to the insertion of CP. The spectrum sensing performance of the cyclostationarity based methods are either similar, or worse than that of the CP method. For both reference and comparison purposes, the OFDM spectrum sensing by the CP method is briefly described in this description. Obviously, the sensing performance of CP-based or cyclostationarity-based spectrum sensing methods depends highly on the length of CP that is inserted. When the CP length is short, a long sensing time is needed to obtain good sensing performance. Motivated by the demand for spectrum sensing in the context of OFDM modulated signals, this description includes the design of a spectrum sensing algorithm based on the Time-Domain Symbol Cross-Correlation (TDSC) of two OFDM symbols. The TDSC algorithm utilizes the property that there is a nonzero constant term embedded in the TDSC if the two OFDM symbols have the same frequency-domain pilot symbols. Thus, the proposed spectrum sensing method can be applied to any OFDM system which allocates frequency-domain pilot symbols to assist in performing synchronization and channel estimation. This description first statistically analyzes the TDSC of two OFDM symbols in which the same frequency-domain pilot symbols are embedded. Based on the TDSC, spectrum sensing algorithms for OFDM systems employing pilot tones are provided. The algorithm and statistical behavior of the TDSC-based spectrum sensors are then explicitly analyzed. The CP method is described next. Finally, the performances of the TDSC and CP methods are evaluated via computer simulations. Four CP ratios are simulated for AWGN, Rayleigh, and Ricean channels as defined in the DVB-T Standard for a sensing time equal to 50 ms and a false alarm probability equal to 0.01. Simulation results show that the TDSC method can achieve misdetection probabilities of 0.1 and 0.01 for SNR values equal to −20.5 dB and −19.5 dB, respectively. Moreover, the TDSC method has approximately the same detection performance for different CP ratios, while the detection performance of the CP method degrades dramatically when the CP ratio becomes small. The TDSC method outperforms the CP method either by 2 dB, or 6 dB when the CP is either 1/4, or 1/32 of the discrete Fourier Transform (DFT) size, respectively.